Additive for non-aqueous liquid electrolyte secondary cell, non-aqueous liquid electrolyte secondary cell, additive for non-aqueous liquid electrolyte electric double layer capacitor and non-aqueous liquid electrolyte electric double layer capacitor

ABSTRACT

The present invention provides additives for a non-aqueous electrolytic solution secondary cell and a non-aqueous electrolytic solution electric double layer capacitor comprising a phosphazene derivative represented by formula (1):  
     (PNF 2 ) n    formula (1)  
     wherein n represents 3 to 14, and provides the non-aqueous electrolytic solution secondary cell and the non-aqueous electrolytic solution electric double layer capacitor each containing a non-aqueous electrolytic solution which has the additive for the non-aqueous electrolytic solution secondary cell or the additive for the non-aqueous electrolytic solution electric double layer capacitor and a supporting salt, an anode, and a cathode.

TECHNICAL FIELD

[0001] The present invention relates to a non-aqueous electrolyticsolution secondary cell and a non-aqueous electrolytic solution electricdouble layer capacitor, which have excellent deterioration resistance,low internal resistance, excellent conductivity because the viscosity ofthe non-aqueous electrolytic solution is low, and excellentlow-temperature characteristics, and to additives used for thenon-aqueous electrolytic solution secondary cell and the non-aqueouselectrolytic solution electric double layer capacitor.

BACKGROUND ART

[0002] Conventionally, nickel-cadmium cells have been the main cellsused as secondary cells for memory-backup or sources for driving AV(Audio Visual) and information devices, particularly personal computers,VTRs (video tape recorders) and the like. Lately, non-aqueouselectrolytic solution secondary cells have been drawing a lot ofattention as a replacement for the nickel-cadmium cells becausenon-aqueous electrolytic solution secondary cells have advantages ofhigh voltage, high energy concentration, and displaying excellentself-dischargeability. Various developments of the non-aqueouselectrolytic solution secondary cells have been performed and a portionof these developments has been commercialized. For example, more thanhalf of notebook type personal computers, cellular phones and the likeare driven by the non-aqueous electrolytic solution secondary cells.

[0003] Carbon is often used as a cathode material in the non-aqueouselectrolytic solution secondary cells, and various organic solvents areused as electrolytic solutions in order to mitigate the risk whenlithium is produced on the surface of cathode, and to increase outputsof driven voltages. Further, particularly in non-aqueous electrolyticsolution secondary cells for use in cameras, alkali metals (especially,lithium metals or lithium alloys) are used as the cathode materials, andaprotic organic solvents such as ester organic solvents are ordinarilyused as the electrolytic solutions.

[0004] However, although these non-aqueous electrolytic solutionsecondary cells exhibit high performance, they are prone todeterioration. Accordingly, a problem occurs in that these non-aqueouselectrolytic solution secondary cells cannot maintain high performancefor a long period of time. For this reason, there has been a high demandfor development of a non-aqueous electrolytic solution secondary cellsin which deterioration is prevented, whereby cell properties such ashigh charging/discharging capacity and high conductivity, and lowinternal resistance can be maintained for a long period of time.

[0005] Further, development has been required of non-aqueouselectrolytic solution secondary cells which have excellentlow-temperature characteristics because cell properties must bemaintained for a long period of time even under low-temperatureconditions such as in the regions or seasons in which the temperature islow.

[0006] On the other hand, a non-aqueous electrolytic solution electricdouble layer capacitor is a condenser making use of electric doublelayers formed between polarizable electrodes and electrolytes. Thenon-aqueous electrolytic solution electric double layer capacitor is aproduct that was developed and commercialized in the 1970s, was in itsinfancy in the 1980s, and has grown and evolved since the 1990s.

[0007] This type of capacitor is different from a cell in which a cycleof an oxidation-reduction reaction accompanied by substance movement isa charging/discharging cycle in that a cycle for electrically absorbing,on a surface of electrodes, ions from electrolytic solutions is acharging/discharging cycle.

[0008] For this reason, the electric double layer capacitor is moreexcellent in instant charging/discharging properties than those of acell. Repeatedly charging/discharging the capacitor does not deterioratethe instant charging/discharging properties.

[0009] Further, in the electric double layer capacitor, since excessivecharging/discharging voltage does not occur during charging/discharging,simple and less expensive electric circuits will suffice for thecapacitor. Moreover, it is easy to know a remaining capacitance in thecapacitor, and the capacitor has endurance under conditions of a widerange of temperature of from −30° C. to 90° C. In addition, thecapacitor is pollution-free, and the like. As described above, thecapacitor is superior to the cell. Consequently, the electric doublelayer capacitor is in the spotlight as a new energy storage product thatis kind to the global environment.

[0010] The electric double layer capacitor is an energy storage devicecomprising positive and negative polarizable electrodes andelectrolytes. At the interface at which the polarizable electrodes andthe electrolytes come into contact with each other, positive andnegative electric charges are arranged so as to face one another and beseparated from one another by an extremely short distance to therebyform an electric double layer. The electrolytes play a role as ionsources for forming the electric double layer. Thus, in the same manneras for the polarizable electrodes, the electrolytes are an essentialsubstance for controlling fundamental properties of the energy storagedevice.

[0011] As the electrolytes, aqueous-electrolytic solutions, non-aqueouselectrolytic solutions, or solid electrolytes are conventionally known.However, from a viewpoint of improvement of energy density of theelectric double layer capacitor, the non-aqueous electrolytic solutionin which a high operating voltage is enabled has particularly been inthe spotlight, and practical use thereof is progressing.

[0012] A non-aqueous electrolytic solution is now put to practical usein which solutes such as (C₂H₅)₄P.BF₄ and (C₂H₅)₄N.BF₄ were dissolved inhighly dielectric solvents such as carbonic acid carbonates (e.g.,ethylene carbonate and propylene carbonate), γ-butyrolactone, and thelike.

[0013] However, although these non-aqueous electrolytic solutionelectric double layer capacitors exhibit high performance, they areprone to deterioration. Accordingly, a problem has been caused in that anon-aqueous electrolytic solution electric double layer capacitor cannotmaintain high performance for a long period of time. For this reason,there has been a high demand for development of a non-aqueouselectrolytic solution electric double layer capacitor in whichoccurrence of deterioration thereon is prevented, whereby capacitorproperties can be maintained for a long period of time.

[0014] Further, there has been a demand for development of a non-aqueouselectrolytic solution electric double layer capacitors which are alsoexcellent in low-temperature characteristics because electriccharacteristics must be maintained for a long period of time even underlow-temperature conditions such as in regions or seasons in which thetemperature is low.

DISCLOSURE OF INVENTION

[0015] It is an object of the present invention to solve theconventional problems described above, meet various needs, andaccomplish the following objects. Namely, an object of the presentinvention is to provide an additive for a non-aqueous electrolyticsolution secondary cell. The additive for the non-aqueous electrolyticsolution secondary cell is added to the non-aqueous electrolyticsolution secondary cell. While maintaining cell properties required forcells, the additive for the non-aqueous electrolytic solution secondarycell is able to make the non-aqueous electrolytic solution secondarycell which has excellent deterioration resistance, in which electricconductivity is high because interface resistance at a non-aqueouselectrolytic solution is low to thereby reduce internal resistance, andwhich has excellent low-temperature characteristics. Further, anotherobject of the present invention is to provide a non-aqueous electrolyticsolution secondary cell which contains therein the additive for thenon-aqueous electrolytic solution secondary cell, which has excellentdeterioration resistance, in which electric conductivity is high becauseinterface resistance at a non-aqueous electrolytic solution is low andinternal resistance is thereby low, and which has excellentlow-temperature characteristics.

[0016] Still another object of the present invention is to provide anadditive for a non-aqueous electrolytic solution electric double layercapacitor. The additive for the non-aqueous electrolytic solutionelectric double layer capacitor is added to the non-aqueous electrolyticsolution electric double layer capacitor. While maintaining sufficientelectric characteristics, the additive for the non-aqueous electrolyticsolution electric double layer capacitor is able to make the non-aqueouselectrolytic solution electric double layer capacitor which hasexcellent deterioration resistance, in which electric conductivity ishigh because interface resistance at a non-aqueous electrolytic solutionis low, and internal resistance is low, and which has excellentlow-temperature characteristics. Further, the object of the presentinvention is to provide a non-aqueous electrolytic solution electricdouble layer capacitor. The non-aqueous electrolytic solution electricdouble layer capacitor contains therein the additive for the non-aqueouselectrolytic solution electric double layer capacitor, and whilemaintaining sufficient electric characteristics such as electricalconductivity, the non-aqueous electrolytic solution electric doublelayer capacitor has excellent deterioration resistance, high electricconductivity because interface resistance at a non-aqueous electrolyticsolution is low and internal resistance is thereby low, and excellentlow-temperature characteristics.

[0017] The present invention provides an additive for a non-aqueouselectrolytic solution secondary cell, which contains therein aphosphazene derivative represented by formula (1):

(PNF₂)_(n)   formula (1)

[0018] In formula (1), n represents 3 to 14.

[0019] Further, the present invention provides a non-aqueouselectrolytic solution secondary cell comprising a non-aqueouselectrolytic solution containing therein the additive for thenon-aqueous secondary cell and supporting salt, an anode, and a cathode.

[0020] Moreover, the present invention provides an additive for anon-aqueous electrolytic solution electric double layer capacitor, whichcontains therein a phosphazene derivative represented by formula (1):

(PNF₂)_(n)   formula (1)

[0021] In formula (1), n is 3 to 14.

[0022] Further, the present invention provides a non-aqueouselectrolytic solution electric double layer capacitor comprising anon-aqueous electrolytic solution containing therein the additive forthe non-aqueous electrolytic solution electric double layer capacitorand a supporting salt, an anode, and a cathode.

BEST MODE FOR CARRYING OUT THE INVENTION

[0023] A more detailed description of the present invention will be madehereinafter.

[0024] 1. Additives for a Non-Aqueous Electrolytic Solution SecondaryCell and a Non-Aqueous Electrolytic Solution Electric Double LayerCapacitor

[0025] Each of the additives for a non-aqueous electrolytic solutionsecondary cell or a non-aqueous electrolytic solution electric doublelayer capacitor of the present invention contains therein a phosphazenederivative, and other components if necessary:

[0026] —Phosphazene Derivative—

[0027] A phosphazene derivative is contained in the additive for thenon-aqueous electrolytic solution secondary cell for the followingreasons:

[0028] In ester-based electrolytic solutions as electrolytic solutionsof a conventional non-aqueous electrolytic solution secondary cell, itis considered that corrosion of the secondary cell occurs and proceedsdue to a PF₅ gas generated when, for example, a lithium ion source suchas an LiPF₆ salt as a supporting salt decomposes into LiF and PF₅ astime goes by, or due to a hydrogen fluoride gas that is generated whenthe generated PF₅ gas further reacts with water or the like. Thus, aphenomenon in which not only conductivity of the non-aqueouselectrolytic solution deteriorates, but also electrode materialsdeteriorate due to the generation of the hydrogen fluoride gas.

[0029] On the other hand, the phosphazene derivative contributes tosuppress decomposition of lithium ion sources such as LiPF₆ salts, andstabilize the same. Accordingly, the phosphazene derivative can be addedto a conventional non-aqueous electrolytic solution to suppressdecomposition reaction of the non-aqueous electrolytic solution, wherebycorrosion and deterioration of the secondary cell can suitably besuppressed.

[0030] Further, the phosphazene derivative is a liquid whose viscosityis low at ordinary temperature (25° C.). Therefore, the addition of theadditive for the non-aqueous electrolytic solution secondary cell of thepresent invention containing therein the phosphazene derivative to thenon-aqueous electrolytic solution secondary cell realizes a non-aqueouselectrolytic solution having a low viscosity, whereby a non-aqueouselectrolytic solution secondary cell having low internal resistance andhaving high conductivity can be provided.

[0031] Moreover, the addition of the additive for a non-aqueouselectrolytic solution secondary cell of the present invention containingtherein the phosphazene derivative to the non-aqueous electrolyticsolution can impart excellent low-temperature characteristics to thenon-aqueous electrolytic solution. Therefore, the present invention canprovide non-aqueous electrolytic solution secondary cells that canexhibit excellent discharging characteristics for a long period of timeeven under low-temperature conditions such as in regions or seasons inwhich the temperature is low.

[0032] Reasons why the phosphazene derivatives are contained in theadditive for the non-aqueous electrolytic solution electric double layercapacitor can be assumed as described below.

[0033] In a conventional non-aqueous electrolytic solution electricdouble layer capacitor, it is considered that compounds generated due todecomposition or reaction of the electrolytic solution or the supportingsalt in the non-aqueous electrolytic solution cause electrodes andperipheral materials of the electrodes to corrode. Or it is alsoconsidered that, since the amount of the supporting salt itselfdecreases due to the decomposition or the reaction, electriccharacteristics are damaged, resulting in deterioration of theperformance of the capacitor.

[0034] On the other hand, the phosphazene derivative contributes tosuppress decomposition or reaction of electrolytic solutions orsupporting salts to stabilize the same (the phosphazene derivativeespecially works well on PF₆ salts). Accordingly, the phosphazenederivative is added to the conventional non-aqueous electrolyticsolution thus making it possible to prevent deterioration of theelectric double layer capacitor while maintaining electriccharacteristics of the capacitor.

[0035] Further, as described above, the phosphazene derivative is aliquid whose viscosity is low at ordinary temperature (25° C.).Therefore, the addition of the additive for the non-aqueous electrolyticsolution double layer capacitor of the present invention, which containstherein the phosphazene derivative, to the non-aqueous electrolyticsolution double layer capacitor realizes the non-aqueous electrolyticsolution having a low viscosity, thus making it possible to provide anon-aqueous electrolytic solution double layer capacitor having lowinternal resistance and high conductivity.

[0036] Moreover, the addition of the additive for the non-aqueouselectrolytic solution double layer capacitor of the present invention,which contains therein the phosphazene derivative to the non-aqueouselectrolytic solution double layer capacitor can provide the non-aqueouselectrolytic solution with excellent low-temperature characteristics.Therefore, it becomes possible to provide a non-aqueous electrolyticsolution double layer capacitor which exhibits excellent electriccharacteristics for a long period of time when used underlow-temperature conditions such as in regions or seasons in which thetemperature is low.

[0037] —Molecular Structure—

[0038] A phosphazene derivative is represented by formula (1):

(PNF₂)_(n)   formula (1)

[0039] In formula (1), n is of 3 to 14.

[0040] In formula (1), from viewpoints that it is possible for thephosphazene derivative represented by formula (1) to provide thenon-aqueous electrolytic solution with excellent low-temperaturecharacteristics, and to lower the viscosity of the non-aqueouselectrolytic solution, n is preferably 3 to 4, and more preferably 3.

[0041] Ordinarily, in a compound containing a halogen element (fluorine)such as the phosphazene derivative described above, there is oftencaused a problem about the formation of halogen radicals. However, withthe phosphazene derivative, such a problem is not caused because aphosphorus element in its molecular structure captures halogen radicalsand forms stable halogenated phosphorus.

[0042] In formula (1), n values are appropriately selected, whereby itbecomes possible to synthesize a non-aqueous electrolytic solutionhaving more preferable viscosity, boiling points, solubility that issuitable for mixture, and low-temperature characteristics. Thesephosphazene derivatives can be used alone or in combination.

[0043] —Flash Point—

[0044] Flash point of the phosphazene derivative is not particularlylimited. However, from a viewpoint of suppression of combustion, it ispreferably 100° C. or more, and more preferably 150° C. or more.

[0045] If the flash point of the phosphazene derivative is 100° C. ormore, combustion or the like can be suppressed. Further, even ifcombustion or the like occurs inside cells or capacitors, it becomespossible to prevent a danger of causing the phosphazene derivative to beignited and combusted to spread over the surface of the electrolyticsolution.

[0046] The “flash point” specifically refers to a temperature at whichflame spreads over the surface of a substance and covers 75% thereof.The flash point can be a criterion to see a tendency at which a mixturethat is combustible with air is formed. In the present invention, avalue measured by a “Mini-flash” method described below is used. Namely,an apparatus (i.e., an automatic flammability measuring device,MINIFLASH manufactured by GRABNER INSTRUMENTS Inc.) comprising a smallmeasuring chamber (4 ml), a heating cup, a flame, an ignition portionand an automatic flame sensing system is prepared in a sealed cupmethod. A sample to be measured (1 ml) is put into the heating cup. Thisheating cup is covered with a cover. The heating cup is heated from theupper portion of the cover. Hereinafter, the temperature of the sampleis arisen at a constant interval, a mixture of vapor and air in the cupis ignited at a constant interval of temperature, and combustion isdetected. The temperature when combustion is detected is regarded as aflash point.

[0047] As each of amounts in which the additives for a non-aqueouselectrolytic solution secondary cell and a non-aqueous electrolyticsolution electric double layer capacitor of the present invention areadded thereto, use of an amount which is equal to a preferable range ofvalues of the content of the phosphazene derivative in a non-aqueouselectrolytic solution secondary cell/a non-aqueous electrolytic solutionelectric double layer capacitor which will be described below ispreferable. The amount of the additive of the present invention iscontrolled to a value within the aforementioned range to suitablyprovide effects of the invention such as deterioration resistance, lowviscosity and low-temperature characteristics of the non-aqueouselectrolytic solution.

[0048] In accordance with the above-described additives for anon-aqueous electrolytic solution secondary cell and a non-aqueouselectrolytic solution electric double layer capacitor of the presentinvention, the addition of the respective additives to the non-aqueouselectrolytic solution secondary cell and the non-aqueous electrolyticsolution electric double layer capacitor can provide additives for anon-aqueous electrolytic solution secondary cell and a non-aqueouselectrolytic solution electric double layer capacitor capable of makinga non-aqueous electrolytic solution secondary cell and a non-aqueouselectrolytic solution electric double layer capacitor, while maintainingcell properties required for cells or sufficient electriccharacteristics required for capacitors, which exhibit excellentdeterioration resistance, low interface resistance at a non-aqueouselectrolytic solution, low internal resistance, and accordingly exhibithigh conductivity, and which exhibit excellent low-temperaturecharacteristics.

[0049] 2. A Non-Aqueous Electrolytic Solution Secondary Cell

[0050] The non-aqueous electrolytic solution secondary cell of thepresent invention comprises an anode, a cathode, and a non-aqueouselectrolytic solution, and if necessary, other member.

[0051] —Anode—

[0052] Materials for anodes are not particularly limited, and can beappropriately selected from any known anode materials, and used.Preferable examples of anode materials include: metal oxides such asV₂O₅, V₆O₁₃, MnO₂, MoO₃, LiCoO₂, LiNiO₂, and LiMn₂O₄; metal sulfidessuch as TiS₂ and MoS₂; and conductive polymers such as polyaniline.Among these, LiCoO₂, LiNiO₂ and LiMn₂O₄ are preferable because they aresafe, have high capacity, and are excellent in wettability with respectto electrolytic solutions. The materials can be used alone or incombination.

[0053] Configuration of the anodes is not particularly limited, and canbe preferably selected from known configurations as electrodes, such assheet, solid-cylindrical, plate and spiral-shaped configurations.

[0054] —Cathode—

[0055] Materials for a cathode are not particularly limited as long asthey can absorb and discharge lithium or lithium ions. The cathode canbe selected appropriately from known cathode materials, and used.Preferable examples of cathode materials include those containinglithium therein such as lithium metal itself; alloys of lithium andaluminum, indium, lead or zinc; and a carbon material such aslithium-doped graphite. Among these materials, a carbon material such asgraphite is preferable from the viewpoint of high safety. Thesematerials can be used alone or in combination.

[0056] Configuration of a cathode is not particularly limited, and canappropriately be selected from known configurations in the same manneras those of the above-described anode.

[0057] —Non-Aqueous Electrolytic Solution—

[0058] A non-aqueous electrolytic solution contains the additive for thenon-aqueous electrolytic solution secondary cell of the presentinvention and a supporting salt and, and, if necessary, othercomponents.

[0059] —Supporting Salt—

[0060] As a supporting salt, ion sources of lithium ions are preferable.ion sources of the lithium ions such as LiClO₄, LiBF₄, LiPF₆, LiCF₃SO₃,LiAsF₆, LiC₄F₉SO₃, Li(CF₃SO₂)₂N, and Li(C₂F₅SO₂)₂N can preferably beused. These can be used alone or in combination.

[0061] An amount in which the supporting salt is contained in thenon-aqueous electrolytic solution (solvent component) (1 kg) ispreferably 0.2 to 1 mol, and more preferably 0.5 to 1 mol.

[0062] If the amount in which the supporting salt is contained in thenon-aqueous electrolytic solution is less than 0.2 mol, sufficientconductivity of the non-aqueous electrolytic solution cannot be secured.Therefore, charging/discharging characteristics of cells may be damaged.Meanwhile, if the amount in which the supporting salt is contained inthe non-aqueous electrolytic solution is more than 1 mol, viscosity ofthe non-aqueous electrolytic solutions increases, sufficient mobility ofthe lithium ion or the like cannot be secured, and sufficientconductivity of the non-aqueous electrolytic solutions cannot be securedas in the above-description. Therefore, charging/dischargingcharacteristics of the cells may be damaged.

[0063] —Additive for a Non-Aqueous Electrolytic Solution Secondary Cell—

[0064] The additive for non-aqueous electrolytic solution secondarycells is that which is the same as in the description about the additivedisclosed in the present invention, and contains therein the phosphazenederivative represented by formula (1).

[0065] —Viscosity—

[0066] Viscosity of a non-aqueous electrolytic solution at 25° C. ispreferably 10 mPa.s (10 cP) or less, more preferably 5 mPa.s (5 cP) orless, and most preferably 4.0 mPa.s (4.0 cP) or less.

[0067] If the viscosity is 10 mPa.s (10 cP) or less, a non-aqueouselectrolytic solution secondary cell having excellent cell propertiessuch as low internal resistance, high conductivity and the like can beobtained.

[0068] Viscosity is measured for 120 minutes at each of rotationalspeeds of 1 rpm, 2 rpm, 3 rpm, 5 rpm, 7 rpm, 10 rpm, 20 rpm and 50 rpmby a viscometer (product name: R-type viscometer Model RE500-SL,manufactured by Toki Sangyo K.K.) and determined on the basis of therotational speed as an analysis condition at which the value indicatedby the viscometer reached 50 to 60%.

[0069] —Conductivity—

[0070] The viscosity of the non-aqueous electrolytic solution isadjusted to the aforementioned preferable range of values, therebyfacilitating the non-aqueous electrolytic solution to have preferableconductivity. In a case of a solution in which lithium salt is dissolvedat the concentration of 0.75 mol/l, the conductivity is preferably 2.0mS/cm or more, and more preferably 5.0 mS/cm or more.

[0071] If the conductivity is 2.0 mS/cm or more, sufficient conductivityof the non-aqueous electrolytic solution can be secured, thus making itpossible to suppress internal resistance of the non-aqueous secondarycell, and also control ascent/descent of potentials duringcharging/discharging thereof.

[0072] The conductivity is a value obtained through a measuring methoddescribed below. Namely, the conductivity is measured underpredetermined conditions (temperature: 25° C., pressure: normalpressure, and moisture percentage: 10 ppm or less) by using aconductivity meter (CDM210 type manufactured by Radio Meter Trading Co.,Ltd.), while applying a constant current of 5 mA to the non-aqueouselectrolytic solution secondary cell.

[0073] As for the conductivity, theoretically, at first, a conductance(Gm) of a non-aqueous electrolytic solution is calculated. From this,influence by a cable resistance (R) is removed to determine aconductance (G) of the electrolytic solution itself. Accordingly, aconductance K=G·K (S/cm) can be determined from the obtained value (G)and the cell constant (K) already known.

[0074] —Content—

[0075] Owing to the effects obtained by containing the phosphazenederivative in the non-aqueous electrolytic solution, a total amount inwhich the phosphazene derivative is contained in the non-aqueouselectrolytic solution comprises: three types of contents comprising: afirst content capable of more preferably providing the non-aqueouselectrolytic solution with “low-temperature characteristics”; a secondcontent capable of more preferably lowering the viscosity of thenon-aqueous electrolytic solution ; and a third content capable of morepreferably providing the non-aqueous electrolytic solution with“deterioration resistance”.

[0076] From the viewpoint of the “low-temperature characteristics”, thefirst content of the phosphazene derivative in the non-aqueouselectrolytic solution is preferably 1 vol % or more, more preferably 3vol % or more, and most preferably 5 vol % or more.

[0077] When the first content is less than 1 vol %, it becomesimpossible to lower the freezing point of a non-aqueous electrolyticsolution sufficiently, thus making it impossible to obtain enoughlow-temperature characteristics.

[0078] Further, the “low-temperature characteristics” are measured andevaluated due to the evaluation of the low-temperature characteristicsdescribed below. Namely, cells are charged at 20° C. under theconditions of a maximum voltage of 4.5V, a minimum voltage of 3.0V, anda charging current of 50 mA. Thereafter, charging/discharging in which adischarging current of 100 mA is discharged is repeated to 50 cycles atlow temperatures (such as 0° C., −10° C., and −20° C.). The dischargingcapacity at low temperature at this time is compared with that measuredat 20° C. to calculate a discharging capacity remaining ratio by thefollowing equation (2). Similarly, the discharging capacity remainingratio is measured and calculated with respect to total three cells todetermine a mean value. Accordingly, low-temperature characteristics areevaluated.

discharging capacity remaining ratio=discharging capacity at lowtemperature/discharging capacity (20° C.)×100(%)   Equation (2)

[0079] The second content of the phosphazene derivative in thenon-aqueous electrolytic solution is preferably 3 to 80 vol % in orderto lower the viscosity of the non-aqueous electrolytic solution, andmore preferably 5 to 80 vol % in order to satisfy both thelow-temperature characteristics and the decrease of viscosity of thenon-aqueous electrolytic solution at high level.

[0080] When the second content is less than 3 vol %, the viscosity ofthe non-aqueous electrolytic solution may not be sufficiently lowered.Besides, due to the descent of the freezing point, effects of thelow-temperature characteristics improved by the addition of thephosphazene derivative to the non-aqueous electrolytic solution may notbe developed. On the other hand, if the content exceeds 80 vol %, sincethe dipole moment is small, and solubility of the supporting saltdeteriorates, excellent cell properties cannot be obtained in somecases.

[0081] From the viewpoint of the “deterioration resistance”, the thirdcontent of the phosphazene derivative in the non-aqueous electrolyticsolution is preferably 2 vol % or more, and more preferably 3 to 75 vol%. Further, from the viewpoint that the third content suffices bothdeterioration resistance and low-temperature characteristics at highlevel, 5 to 75 vol % is more preferable.

[0082] If the content is within the aforementioned range of values,deterioration can suitably be suppressed.

[0083] “Deterioration” refers to decomposition of a supporting salt (forexample, lithium salt), and effects due to prevention of thedeterioration are evaluated by an evaluation method of stabilitydescribed below.

[0084] (1) First, the non-aqueous electrolytic solution containing asupporting salt is prepared. Thereafter, moisture content of this ismeasured. Then, concentration of a hydrogen fluoride in the non-aqueouselectrolytic solution is measured by a high performance liquidchromatography (ion chromatography). Further, hues of the non-aqueouselectrolytic solution are visually observed. Thereafter,charging/discharging capacity is calculated by a charging/dischargingtest.

[0085] (2) The non-aqueous electrolytic solution is left in a gloved boxfor 2 months. Thereafter, moisture content and concentration of ahydrogen fluoride are measured again, hues are visually observed, andcharging/discharging capacity is calculated. In accordance withvariations of the obtained values, stability of the non-aqueouselectrolytic solution is evaluated.

[0086] —Other Component—

[0087] As the other component, an aprotic organic solvent and the likeare particularly preferable in respect of safety.

[0088] If an aprotic organic solvent is contained in the non-aqueouselectrolytic solution, since the aprotic organic solvent never reactwith the above-described cathode materials, high safety can be ensured,and the lowering of viscosity of the non-aqueous electrolytic solutionis enabled, thereby facilitating the non-aqueous electrolytic solutionto easily attain optimum ionic conductivity as the non-aqueouselectrolytic solution secondary cell.

[0089] Examples of the aprotic organic solvents are not particularlylimited, but include: ether compounds and ester compounds from theviewpoint of the lowering of viscosity of the non-aqueous electrolyticsolution, and specific examples thereof include: 1,2-dimethoxyethane,tetrahydrofuran, dimethyl carbonate, diethyl carbonate, diphenylcarbonate, ethylene carbonate, propylene carbonate, γ-butyrolactone,γ-valerolactone, and methyl ethyl carbonate.

[0090] Among these, cyclic ester compounds such as ethylene carbonate,propylene carbonate, and y-butyrolactone, chain ester compounds such as1,2-dimethoxyethane, dimethyl carbonate, ethyl methyl carbonate, anddiethyl carbonate are preferable. The cyclic ester compounds arepreferable in that they have high relative dielectric constants and candissolve easily lithium salts or the like, and the chain ester compoundsare preferable in that they have low viscosity, and are able to lowerthe viscosity of the non-aqueous electrolytic solution. These can beused alone. However, use of two or more of these in combination ispreferable.

[0091] —Viscosity of an Aprotic Organic Solvent—

[0092] Viscosity of the aprotic organic solvent at 25° C. is preferably10 mPa.s (10 cP) or less, and more preferably 5 mPa.s (5 cP) or less inorder to easily lower the viscosity of the non-aqueous electrolyticsolution.

[0093] —Other Member—

[0094] As other member, a separator that is interposed between a cathodeand an anode in order to prevent a short circuit of electric currents byboth the cathode and anode contacting to each other, and known membersgenerally used in cells are preferably used.

[0095] Examples of materials for a separator include materials which areable to reliably prevent both electrodes from contacting each other andto include electrolytic solutions therein or flow the same therethrough.Specific examples of the materials include: synthetic resin non-wovenfabrics such as polytetrafluoroethylene, polypropylene, andpolyethylene, thin films, and the like. Among these, use of amicro-porous polypropylene or polyethylene film having a thickness offrom 20 to 50 μm is particularly preferable.

[0096] <Internal Resistance of a Non-Aqueous Electrolytic SolutionSecondary Cell>

[0097] An internal resistance (Ω) of a non-aqueous electrolytic solutionsecondary cell can easily have a preferable value due to the control ofthe viscosity of the non-aqueous electrolytic solution to theaforementioned preferable range of values. The internal resistance (Ω)is preferably 0.1 to 0.3 (Ω), and more preferably 0.1 to 0.25 (Ω).

[0098] The internal resistance can be obtained by a known method such asthe method described below in which internal resistance is measured.Namely, when the non-aqueous electrolytic solution secondary cell ismade and charging/discharging curves are measured, the internalresistance can be obtained by a deflection width of potentials inaccordance with charging rest or discharging rest.

[0099] <Capacity of a Non-Aqueous Electrolytic Solution Secondary Cell>

[0100] When LiCoO₂ is an anode, the capacity (charging/dischargingcapacity) (mAh/g) of the non-aqueous electrolytic solution secondarycell is preferably 140 to 145 (mAh/g), and more preferably 143 to 145(mAh/g).

[0101] A known method is used for measuring the charging/dischargingcapacity, such as the one in which a charging/discharging test iscarried out by using a semi-open type cell or a closed type coin cell(See Masayuki Yoshio, “Lithium ion secondary cell” published by NikkanKogyo Shinbun-sha), whereby a capacity is determined by charging current(mA), time (t) and weight of an electrode material (g).

[0102] <Shape of a Non-Aqueous Electrolytic Solution Secondary Cell>

[0103] The shape of a non-aqueous electrolytic solution secondary cellis not particularly limited and is suitably formed into various knownconfigurations such as a coin-type cell, a button-type cell, apaper-type cell, a square-type cell and a cylindrical cell having aspiral structure.

[0104] In the case of the spiral structure, a sheet type anode isprepared to sandwich a collector, and a (sheet type) cathode issuperimposed on this, and rolled up, whereby a non-aqueous electrolyticsolution secondary cell can be prepared.

[0105] <Performance of a Non-Aqueous Electrolytic Solution SecondaryCell>

[0106] The non-aqueous electrolytic solution secondary cell of thepresent invention is excellent in deterioration resistance, has thenon-aqueous electrolytic solution with low interface resistance, and haslow internal resistance to thereby increase conductivity, and is alsoexcellent in low-temperature characteristics.

[0107] 3. Non-Aqueous Electrolytic Solution Electric Double LayerCapacitor

[0108] The non-aqueous electrolytic solution electric double layercapacitor of the present invention comprises an anode, a cathode, anon-aqueous electrolytic solution, and, if necessary, other member.

[0109] —Anode—

[0110] Materials for an anode of non-aqueous electrolytic solutionelectric double layer capacitors are not particularly limited. However,use of carbon based-polarizable electrodes is generally preferable. Asthe polarizable electrodes, it is preferable to use electrodes in whichspecific surface and/or bulk concentration thereof are large, which areelectro-chemically inactive, and which have a low resistance.

[0111] The polarizable electrodes are not particularly limited. However,the polarizable electrodes generally contain an activated carbon, and ifnecessary, other component such as a conductive agent or a binder.

[0112] —Activated Carbon—

[0113] Raw materials for an activated carbon are not particularlylimited, and typical examples thereof include phenol resins, varioustypes of heat-resistant resins, pitches, and the like.

[0114] Preferable examples of the heat-resistant resins include:polyimide, polyamide, polyamideimide, polyether, polyetherimide,polyetherketone, bismaleicimidetriazine, aramide, fuluoroethylene resin,polyphenylene, polyphenylene sulphide, and the like. These resins can beused alone or in combination.

[0115] It is preferable that an activated carbon used for the anode isformed in powders, fibers, and the like in order to increase thespecific surface area of the electrode and increase the chargingcapacity of the non-aqueous electrolytic solution electric double layercapacitor.

[0116] Further, the activated carbon may be subjected to a heattreatment, a drawing treatment, a vacuum treatment at high temperature,and a rolling treatment for a purpose to increase the charging capacityof the non-aqueous electrolytic solution electric double layercapacitor.

[0117] —Other Component (a Conductive Agent and a Binder)—

[0118] The conductive agent is not particularly limited, but graphiteand acetylene black and the like can be used.

[0119] Materials of the binder are not particularly limited, but resinssuch as polyvinylidene fluoride and tetrafluoroethylene can be used.

[0120] —Cathode—

[0121] As a cathode, polarizable electrodes similar to those for theanode can be preferably used.

[0122] —Non-Aqueous Electrolytic Solution—

[0123] The non-aqueous electrolytic solution contains an additive forthe non-aqueous electrolytic solution electric double layer capacitor, asupporting salt, and, if necessary, other component.

[0124] —Supporting Salt—

[0125] A supporting salt can be selected from those that areconventionally known. However, use of a quaternary ammonium salt, whichcan provides excellent electric characteristics such as electricconductivity and the like in the non-aqueous electrolytic solution, ispreferable.

[0126] The quaternary ammonium salt is required to be a quaternaryammonium salt that is able to form a multivalent ion, in that thequaternary ammonium salt is a solute which acts as an ion source forforming an electric double layer in the non-aqueous electrolyticsolution, and is also able to effectively increase electriccharacteristics such as electric conductivity of the non-aqueouselectrolytic solution.

[0127] Examples of the quaternary ammonium salts include: (CH₃) ₄N.BF₄,(CH₃)₃C₂H₅N.BF₄, (CH₃)₂(C₂H₅)₂N.BF₄, CH₃(C₂H₅)₃N.BF₄, (C₂H₅)₄N.BF₄,(C₃H₇)₄N.BF₄, CH₃(C₄H₉)₃N.BF₄, (C₄)₄N.BF₄, (C₆H₁₃)₄N.BF₄, (C₂H₅)₄N.ClO₄,(C₂H₅)₄N.BF₄, (C₂H₅)₄N.PF₆, (C₂H₅)₄N.AsF₆, (C₂H₅)₄N.SbF₆,(C₂H₅)₄N.CF₃SO₃, (C₂H₅)₄N.C₄F₉SO₃, (C₂H₅)₄N.(CF₃SO₂) ₂N,(C₂H₅)₄N.BCH₃(C₂H₅)₃, (C₂H₅)₄N.B (C₂H₅)₄, (C₂H₅)₄N.B(C₆H₅)₄ and thelike. Further, a hexafluorophosphate of the quaternary ammonium salt maybe used. Moreover, solubility can be improved by increasingpolarizability. Therefore, a quaternary ammonium salt can be used inwhich different alkyl groups are bonded to a nitrogen atom.

[0128] Examples of the quaternary ammonium salt include compoundsrepresented by the following structural formulae (1) to (10):

[0129] In the above-described structural formulae, Me represents amethyl group, and Et represents an ethyl group.

[0130] Among these quaternary ammonium salts, salts which are able togenerate (CH₃)₃N⁺ or (C₂H₅)₄N⁺ as positive ions are preferable in thathigh electric conductivity can be secured. Further, salts which are ableto generate negative ions whose formula weight is small are preferable.

[0131] These quaternary ammonium salts can be used alone or incombination.

[0132] The amount of the supporting salt in the non-aqueous electrolyticsolution (solvent component) (1 kg) is preferably 0.2 to 1.5 mol, andmore preferably 0.5 to 1.0 mol.

[0133] If the amount of the supporting salt in the non-aqueouselectrolytic solution is less than 0.2 mol, electric characteristicssuch as sufficient electric conductivity of the non-aqueous electrolyticsolution can be secured in some cases. On the other hand, if the amountof the supporting salt in the non-aqueous electrolytic solution exceeds1.5 mol, viscosity of the non-aqueous electrolytic solution increasesand electric characteristics such as electric conductivity may decrease.

[0134] —Additive for a Non-Aqueous Electrolytic Solution Electric DoubleLayer Capacitor—

[0135] The additive for a non-aqueous electrolytic solution electricdouble layer capacitor is the same as that in the paragraph of “theadditive for a non-aqueous electrolytic solution electric double layercapacitor of the present invention”, and contains the phosphazenederivative represented by formula (1).

[0136] —Viscosity—

[0137] The viscosity of the non-aqueous electrolytic solution at 25° C.is preferably 10 mPa.s (10 cP) or less, more preferably 5 mPa.s (5 cP)or less, and most preferably 4.0 mPa.s (4.0 cP) or less.

[0138] If the viscosity is 10 mPa.s (10 cP) or less, a non-aqueouselectrolytic solution electric double layer capacitor can be providedwith excellent electric characteristics such as low internal resistance,high conductivity and the like.

[0139] In the present invention, viscosity is measured for 120 minutesat each of rotational speeds of 1 rpm, 2 rpm, 3 rpm, 5 rpm, 7 rpm, 10rpm, 20 rpm and 50 rpm by a viscometer (product name: R-type viscometerModel RE500-SL, manufactured by Toki Sangyo K.K.) and determined on thebasis of the rotational speed as an analysis condition at which thevalue indicated by the viscometer reached 50 to 60%.

[0140] —Conductivity—

[0141] The viscosity of the non-aqueous electrolytic solution can becontrolled to the aforementioned preferable range of values to make iteasy for the non-aqueous electrolytic solution to have a preferablevalue of conductivity. The conductivity of the non-aqueous electrolyticsolution (i.e., as the conductivity of quaternary ammonium saltsolution: 1 mol/kg) is preferably is 2.0 mS/cm or more, and morepreferably 5.0 mS/cm or more.

[0142] If the conductivity is 2.0 mS/cm or more, since sufficientconductivity of the non-aqueous electrolytic solution can be secured, itbecomes possible to suppress internal resistance of the non-aqueouselectrolytic solution double layer capacitor, and control ascent/descentof potentials during charging/discharging thereof.

[0143] The conductivity is a value obtained through a measuring methoddescribed below. Namely, the conductivity is measured underpredetermined conditions (temperature: 25° C., pressure: normalpressure, and moisture percentage: 10 ppm or less) by using aconductivity meter (CDM210 type manufactured by Radio Meter Trading Co.,Ltd.), while applying a constant current of 5 mA to the non-aqueouselectrolytic solution secondary cell.

[0144] Theoretically, at first, a conductance (Gm) of a non-aqueouselectrolytic solution is calculated. From this, an influence by a cableresistance (R) is removed to determine a conductance (G) of theelectrolytic solution itself. Accordingly, a conductance K=G·K (S/cm)can be determined from the obtained value (G) and the cell constant (K)already known.

[0145] —Content—

[0146] Owing to the effects obtained by containing the phosphazenederivative in the non-aqueous electrolytic solution, a total amount inwhich the phosphazene derivative is contained in the non-aqueouselectrolytic solution comprises three types of contents comprising: afirst content capable of more preferably providing the non-aqueouselectrolytic solution with “low-temperature characteristics”; a secondcontent capable of more preferably “lowering the viscosity of thenon-aqueous electrolytic solution”; and a third content capable of morepreferably providing the non-aqueous electrolytic solution with“deterioration resistance”.

[0147] From the viewpoint of the “low-temperature characteristics”, thefirst content of the phosphazene derivative in the non-aqueouselectrolytic solution is preferably 1 vol % or more, more preferably 3vol % or more, and most preferably 5 vol % or more.

[0148] When the first content is less than 1 vol %, it becomesimpossible to sufficiently lower the freezing point of a non-aqueouselectrolytic solution, whereby low-temperature characteristics areinsufficient.

[0149] Further, the “low-temperature characteristics” can be evaluatedby measuring internal resistances (Ω) at 0° C., −5° C., and −10° C.,respectively, and comparing the obtained values with the internalresistance (Ω) measured at 20° C.

[0150] From the viewpoint of the “lowering of the viscosity of thenon-aqueous electrolytic solution”, the second content of thephosphazene derivative in the non-aqueous electrolytic solution ispreferably 3 to 80 vol % or more.

[0151] When the second content is less than 3 vol %, the viscosity ofthe non-aqueous electrolytic solution may not be lowered sufficiently.Besides, as for the descent of the freezing point, effects of thelow-temperature characteristics improved by the addition of thephosphazene derivative to the non-aqueous electrolytic solution may notbe developed. On the other hand, if the content exceeds 80 vol %, sincethe dipole moment is small, and solubility of the supporting saltdeteriorates, excellent electric properties cannot be provided in somecases.

[0152] From the viewpoint of the “deterioration resistance”, the thirdcontent of the phosphazene derivative in the non-aqueous electrolyticsolution is preferably 2 vol % or more, and more preferably 3 to 75 vol%. Further, from a viewpoint that suffices both deterioration resistanceand low-temperature characteristics at high level, the content of thephosphazene derivative is more preferably 5 to 75 vol %.

[0153] If the content is within the aforementioned range of values,deterioration can suitably be suppressed.

[0154] “Deterioration” refers to decomposition of a supporting salt, andeffects due to prevention of the deterioration are evaluated by anevaluation method of stability described below.

[0155] —Other Component—

[0156] As other component, an aprotic organic solvent or the like isparticularly preferable from the viewpoint of safety.

[0157] When the aprotic organic solvent is contained in the non-aqueouselectrolytic solution, the lowering of viscosity of the non-aqueouselectrolytic solution and improvement of electric conductivity areeasily accomplished.

[0158] The aprotic organic solvents are not particularly limited, andthe examples in the above description can be used. Among these, cyclicester compounds such as ethylene carbonate, propylene carbonate, andγ-butyrolactone, chain ester compounds such as 1,2-dimethoxyethane,dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate arepreferable. The cyclic ester compounds are preferable in that they havehigh relative dielectric constants and can dissolve easily thesupporting salt, and the chain ester compounds are preferable in thatthey have low viscosity, and are able to lower the viscosity of thenon-aqueous electrolytic solution. These can be used alone or incombination.

[0159] —Viscosity of an Aprotic Organic Solvent—

[0160] Viscosity of the aprotic organic solvent at 25° C. is preferably10 mPa.s (10 cP) or less, and more preferably 5 mPa.s (5 cP) or less inorder to easily lower the viscosity of the non-aqueous electrolyticsolution.

[0161] —Other Member—

[0162] Examples of other material can include a separator, a collectorand a container.

[0163] The separator is interposed between a cathode and an anode inorder to prevent a short-circuit of the non-aqueous electrolyticsolution electric double layer capacitor. The separator is notparticularly limited, and known separator can preferably be used for thenon-aqueous electrolytic solution electric double layer capacitors.

[0164] Microporous film, nonwoven fabric and paper can preferably beused as the materials for a separator, and specific examples thereofinclude: nonwoven fabrics, thin film layers and the like made fromsynthetic resins such as polytetrafluoroethylene, polypropylene,polyethylene and the like. Among these, polypropylene or polyethylenemicroporous film having a thickness of about 20 to 50 μm is particularlypreferable.

[0165] The collector is not particularly limited, and a known collectorwhich is ordinarily used for non-aqueous electrolytic solution electricdouble layer capacitors is preferably used. The collector is preferablewhich has excellent electrochemical corrosion resistance, chemicalcorrosion resistance, workabilty, and mechanical strength, and which canbe manufactured inexpensively, and preferable examples thereof includealuminum, stainless steel, conductive resins, and the like.

[0166] The container is not particularly limited, and a conventionallyknown container for the non-aqueous electrolytic solution electricdouble layer capacitor is preferably used.

[0167] Materials such as aluminum, stainless steel, conductive resin andthe like are preferably used for the container.

[0168] As the other member than the separator, collector and container,each of known members which are generally used for non-aqueouselectrolytic solution electric double layer capacitor are preferablyused.

[0169] —Internal Resistance of a Non-Aqueous Electrolytic SolutionElectric Double Layer Capacitor—

[0170] The internal resistance (Ω) of a non-aqueous electrolyticsolution electric double layer capacitor is preferably 0.1 to 0.3 (Ω),and more preferably 0.1 to 0.25 (Ω).

[0171] The internal resistance can be obtained by a known method such asthe method described below in which internal resistance is measured.Namely, when the non-aqueous electrolytic solution electric double layercapacitor is made and charging/discharging curves are measured, theinternal resistance can be obtained by a deflection width of potentialsin accordance with charging rest or discharging rest.

[0172] —Configuration and Use of a Non-Aqueous Electrolytic SolutionElectric Double Layer Capacitor—

[0173] Configurations of the non-aqueous electrolytic solution electricdouble layer capacitors are not particularly limited, and conventionallyknown configurations such as cylinder-type (cylindrical or square) orflat-type (coin) are preferably used.

[0174] The non-aqueous electrolytic solution electric double layercapacitors are preferably used for power supplies for memory back-up ofvarious electronic devices, industrial apparatuses, and aeronauticalapparatuses; electric magnetic holders for toys, cordless apparatuses,gas apparatuses, and instant boilers; and clocks such as wrist watch, awall clock, a solar clock, and an AGS (automatic gain stabilization)wrist watch.

[0175] —Performance of a Non-Aqueous Electrolytic Solution ElectricDouble Layer Capacitor—

[0176] The non-aqueous electrolytic solution electric double layercapacitor of the present invention is excellent in deteriorationresistance, and has high conductivity because interface resistance ofthe non-aqueous electrolytic solution is low and internal resistance isthereby low, and is also excellent in low temperature characteristics.

EXAMPLES

[0177] With reference to Examples and Comparative Examples, a moredetailed description of the present invention will be given hereinafter.The present invention is not limited to Examples described below:

Example 1

[0178] [Preparation of a Non-Aqueous Electrolytic Solution]

[0179] 2 ml (2 vol %) of a phosphazene derivative (a cyclic phosphazenederivative represented by formula (1) in which n is 3)(i.e., an additivefor a non-aqueous electrolytic solution secondary cell) was added to 98ml of a mixed solvent of diethyl carbonate and ethylene carbonate(mixture ratio (i.e., volume ratio): diethyl carbonate/ethylenecarbonate=1/1) (aprotic organic solvent). Further, LiPF₆ (supportingsalt) was dissolved in this mixture at concentration of 0.75 mol/kg,whereby a non-aqueous electrolytic solution (viscosity at 25° C.: 3.6mPa.s (3.6 cP), conductivity of 0.75 mol/l of a lithium salt dissolvedsolution: 7.5 mS/cm) was prepared.

[0180] The viscosity and conductivity of the non-aqueous electrolyticsolution were respectively measured by the measuring method describedabove.

[0181] <Evaluation of Deterioration>

[0182] Deterioration was evaluated with respect to the obtainednon-aqueous electrolytic solution in the same manner as the evaluationmethod of stability such that moisture percentage (ppm), concentrationof hydrogen fluoride (ppm), and charging/discharging capacity (mAh/g) ofthe non-aqueous electrolytic solution were measured and calculated,immediately after the non-aqueous electrolytic solution was prepared,and after the non-aqueous electrolytic solution was left in a gloved boxfor two months. At this time, the charging/discharging capacity (mAh/g)was determined such that a charging/discharging curve was measured byusing an anode whose weight has already been known, or theaforementioned cathode, and the obtained charging amounts anddischarging amounts were divided by the weight of electrodes used.Further, change of hues of the non-aqueous electrolytic solutionobtained immediately after the non-aqueous electrolytic solution wasprepared and after the non-aqueous electrolytic solution was left in thegloved box for two months was visually observed. The results are shownin table 1.

[0183] [Preparation of a Non-Aqueous Electrolytic Solution SecondaryCell]

[0184] A cobalt oxide represented by chemical formula LiCoO₂ was used asan anode active substance. 10 parts of acetylene black (conductiveassistant) and 10 parts of teflon binder (binder resin) were added to100 parts of LiCoO₂. This was kneaded with an organic solvent (a mixtureof ethyl acetate and ethanol in a ratio of 50 to 50 wt %). Thereafter,this was press-rolled to form a thin anode sheet (thickness: 100 μm andwidth: 40 mm).

[0185] Thereafter, an aluminum foil (collector), to the surface of whicha conductive adhesive was applied and which had a thickness of 25 μm,was sandwiched by the two anode sheets thus obtained. A separator (amicroporous polypropylene film) having a thickness of 25 μm was putthereon, and a lithium metal foil having a thickness of 150 μm wassuperimposed thereon, and then rolled up to thereby make a cylindricalelectrode. The cylindrical electrode had an anode length of about 260mm.

[0186] The cylindrical electrode was impregnated with the non-aqueouselectrolytic solution, and sealed to thereby form a size AA lithiumcell.

[0187] <Measurement and Evaluation of Cell Properties>

[0188] After initial properties (such as voltage and internalresistance) of the cell obtained were measured and evaluated at 20° C.,charging/discharging cycle performance was measured and evaluated by amethod of evaluation described below. The results are shown in table 1.

[0189] <<Evaluation of Charging/Discharging Cycle Performance>>

[0190] Charging/discharging were repeated to 50 cycles, providing that amaximum voltage was 4.5V, a minimum voltage was 3.0V, a dischargingcurrent was 100 mA, and a charging current was 50 mA. Acharging/discharging capacity at this time was compared with that at theinitial stage of charging/discharging, and a capacity remaining ratioafter charging/discharging was repeated 50 times was calculated.Similarly, the capacity remaining ratio for total three cells wasmeasured and calculated to determine a mean value to thereby evaluatecharging/discharging characteristics.

[0191] <Evaluation of Characteristics at Low Temperature (Measurement ofCapacity at Low Temperature)>

[0192] Charging/discharging of the obtained cells was repeated to 50cycles under the same conditions as the aforementioned “Evaluation ofcharging/discharging characteristics” except that discharging wasconducted at low temperature (such as 0° C., −10° C., and −20° C.). Adischarging capacity at such low temperature at this time was comparedwith that measured at 20° C. to thereby calculate a discharging capacityremaining ratio by using the equation below. The discharging capacityremaining ratio was measured and calculated with respect to total threecells, whereby a mean value was determined to evaluate dischargingcharacteristics at low temperature. The results arc shown in table 1.

Discharging capacity remaining ratio=discharging capacity at lowtemperature/discharging capacity (20° C.)×100 (%)   Equation (2)

Example 2

[0193] Except that the amount of the mixed solvent of diethyl carbonateand ethylene carbonate was changed to 99 ml, and that of the phosphazenederivative was changed to 1 ml (1 vol %) in the “Preparation of anon-aqueous electrolytic solution” in Example 1, a non-aqueouselectrolytic solution (viscosity at 25° C.: 3.6 mPa.s (3.6 cP), andconductivity of 0.75 mol/l of a lithium salt dissolved solution: 7.6mS/cm) was prepared in the same manner as that in Example 1, wherebydeterioration resistance was evaluated. Further, a non-aqueouselectrolytic solution secondary cell including the non-aqueouselectrolytic solution was made in the same manner as in Example 1, andinitial cell properties (such as voltages and internal resistances),charging/discharging cycle performance, and low-temperaturecharacteristics thereof were respectively measured and evaluated. Theresults are shown in table 1.

Comparative Example 1

[0194] Except that the phosphazene derivative was replaced by aphosphazene derivative (i.e., a cyclic phosphazene derivative obtainedby replacing six Fs of a compound represented by formula (1) in which nis 3, with six methoxyethoxyethoxy groups) in the “Preparation of thenon-aqueous electrolytic solution” in Example 1, a non-aqueouselectrolytic solution (viscosity at 25° C.: 8.0 mPa.s (8.0 cP), andconductivity of 0.75 mol/l of a lithium salt solution: 6.0 mS/cm) wasprepared in the same manner as that in Example 1, whereby deteriorationresistance was evaluated. Further, a non-aqueous electrolytic solutionsecondary cell containing this non-aqueous electrolytic solution wasmade in the same manner as in Example 1, and initial cell properties(such as voltages and internal resistances), charging/discharging cycleperformance, and low-temperature characteristics thereof wererespectively measured and evaluated. The results are shown in table 1.TABLE 1 After preparation of After left for 2 months (in Cell propertieselectrolytic solution (Evaluation gloved box) (Evaluation(charging/discharging of deterioration) of deterioration) capacity(mAh/g)) Charging/ Charging/ After After 50 discharging HF Moisturedischarging HF Moisture Evaluation initial cycles of Exam- capacitycontents percentage capacity contents percentage Change of of charging/charging/ ples (mAh/g) (ppm) (ppm) (mAh/g) (ppm) (ppm) huesdeterioration discharging discharging Ex. 1 147 2 2 147 3 2 noneExtremely 147 145 stable Ex. 2 146 2 2 146 2 2 light stable 146 145yellow Com. 143 1 2 142 1 2 none stable 144 140 Ex. 1 Evaluation oflow-temperature characteristics (discharging capacity remaining ratio(%) after 50 cycles) Cell Viscosity of non- Viscosity of non-Conductivity 0° C. −10° C. −20° C. pro- aqueous electrolytic aqueouselectrolytic of non- during during during Cell properties pertiessolution (before adding solution aqueous Exam- dis- dis- dis- (initialinternal (initial supporting salt) at at 25° C. electrolytic plescharging charging charging resistance (Ω) voltage) 25° C. (mPa · s(cP))(mPa · s(cP)) solution (mS/cm) Ex. 1 95 70 50 0.09 2.65 1.8 3.6 7.5 Ex.2 95 60 50 0.09 2.65 1.8 3.6 7.6 Com. 70 50 30 0.18 2.8  3.2 8.0 6.0 Ex.1

Example 3

[0195] [Preparation of a Non-Aqueous Electrolytic Solution]

[0196] 2 ml (2 vol %) of a phosphazene derivative (a cyclic phosphazenederivative represented by formula (1) in which n is 3)(i.e., an additivefor a non-aqueous electrolytic solution electric double layer capacitor)was added to 98 ml of propylene carbonate (aprotic organic solvent).Further, tetraethyl ammonium fluoroborate (C₂H₅)₄N.BF₄ (supporting salt)was dissolved in this mixture at the concentration of 1 mol/kg, wherebya non-aqueous electrolytic solution (viscosity at 25° C.: 3.8 mPa.s (3.8cP) was prepared.

[0197] <Evaluation of Deterioration>

[0198] Deterioration was evaluated, in the same manner as the evaluationmethod of stability, such that moisture percentage (ppm), concentrationof hydrogen fluoride (ppm), and internal resistance (Ω) of thenon-aqueous electrolytic solution were measured and calculated at 20° C.immediately after the non-aqueous electrolytic solution was prepared andafter the non-aqueous electrolytic solution was left in a gloved box fortwo months. At this time, the internal resistance (Ω) was determinedsuch that a charging/discharging curve was measured by using an anodewhose weight has already been known, or the aforementioned cathode, andthe obtained charging amounts and discharging amounts were divided bythe weight of electrodes. Further, change of hues of the non-aqueouselectrolytic solution obtained immediately after the non-aqueouselectrolytic solution was prepared and after the non-aqueouselectrolytic solution was left in the gloved box for two months wasvisually observed. The results are shown in table 2.

[0199] [Preparation of Anodes/Cathodes (Polarizable Electrodes)]

[0200] Activated carbon (Kuractive-1500 manufactured by Kuraray ChemicalCo., Ltd), acetylene black (conductive agent) and tetrafluoroethylene(PTFE) (binder) were mixed with each other so that a massive ratio(activated carbon/acetylene black/PTFE) was 8/1/1, whereby a mixture wasobtained.

[0201] 100 mg of the obtained mixture was sampled, and contained in apressure tight carbon container (20 mmφ), and pressed powder was formedfrom the mixture at a pressure of 150 kgf/cm² and at room temperature,whereby anodes and cathodes (polarizable electrodes) were made.

[0202] [Preparation of a Non-Aqueous Electrolytic Solution Double LayerCapacitor]

[0203] The obtained anodes and cathodes, and aluminum metal plate(collector) (thickness: 0.5 mm), and polypropylene/polyethylene plate(separator) (thickness: 25 μm) were used to assemble a cell. The cellwas sufficiently vacuum-dried.

[0204] The cell was impregnated with the non-aqueous electrolyticsolution, whereby a non-aqueous electrolytic solution electric doublelayer capacitor was prepared.

[0205] [Measurement of Electric Conductivity of a Non-AqueousElectrolytic Solution Electric Double Layer Capacitor]

[0206] While a constant current (5 mA) was flown into the obtainedcapacitor, electric conductivity of the capacitor was measured by aconductivity meter (CDM210 manufactured by Radio Meter Trading Co.,Ltd.) The results are shown in table 2.

[0207] Further, if the electric conductivity of the non-aqueouselectrolytic solution electric double layer capacitor at 25° C. is 5.0mS/cm or more, it is a level that does not cause a practical problem.

[0208] [Evaluation of Low-Temperature Characteristics]

[0209] Further, with respect to the obtained non-aqueous electrolyticsolution electric double layer capacitor, internal resistance (φ)thereof was measured at 0° C., −5° C., and −10° C., respectively, andcompared with the internal resistance (φ) that was measured at 20° C.,and evaluated. Respective internal resistances (Ω) at 0° C., −5° C., and−10° C. are shown in table 2.

Example 4

[0210] Except that the amount of propylene carbonate was changed to 99ml, and that of the phosphazene derivative was changed to 1 ml (1 vol %)in the “Preparation of a non-aqueous electrolytic solution” in Example3, a non-aqueous electrolytic solution (viscosity at 25° C.: 3.9 mPa.s(3.9 cP) was prepared in the same manner as that in Example 3, wherebydeterioration was evaluated. Further, a non-aqueous electrolyticsolution electric double layer capacitor containing this non-aqueouselectrolytic solution was made in the same manner as that in Example 3,and electric conductivity and low-temperature characteristics thereofwere respectively measured and evaluated. The results are shown in table2.

Comparative Example 2

[0211] Except that the phosphazene derivative was replaced by aphosphazene derivative (i.e., a cyclic phosphazene derivative obtainedby replacing six Fs of a compound represented by formula (1) in which nis 3 with six methoxyethoxyethoxy groups) in the “Preparation of thenon-aqueous electrolytic solution” in Example 3, a non-aqueouselectrolytic solution (viscosity at 25° C.: 8.0 mPa.s (8.0 cP)) wasprepared in the same manner as that in Example 3, whereby deteriorationwas evaluated. Further, a non-aqueous electrolytic solution electricdouble layer capacitor containing this non-aqueous electrolytic solutionwas made in the same manner as in Example 3, and electric conductivityand low-temperature characteristics thereof were respectively measuredand evaluated. The results are shown in table 2. TABLE 2 Afterpreparation of After left for 2 months (in electrolytic solution(Evaluation gloved box) (Evaluation of deterioration) of deterioration)Internal HF Moisture Internal HF Moisture resistance contents percentageresistance contents percentage Change Evaluation of Examples (Ω) (ppm)(ppm) (Ω) (ppm) (ppm) of hues deterioration Example 0.10 less 2 0.10less 2 none extremely 3 than 1 than 1 stable ppm ppm Example 0.10 less 20.10 less 2 light Stable 4 than 1 than 1 yellow ppm ppm Com. 0.10 less 10.10 less 2 none stable Example than 1 than 1 2 ppm ppm Evaluation oflow-temperature characteristics (Ω) Viscosity of non- Viscosity of non-Conductivity of aqueous electrolytic aqueous non-aqueous InternalInternal Internal solution (before electrolytic electrolytic resistan ceresistan ce resistan ce adding solution solution (Ω) (Ω) (Ω) supportingsalt) (25° C.) (25° C.) Examples (0° C.) (−5° C.) (−10° C.) (25° C.)(mPa · s) (mPa · s) (mS/cm) Example 0.15 0.22 0.25 2.4 3.8 7.6 3 Example0.16 0.23 0.28 2.5 3.9 7.4 4 Com. 0.22 0.30 0.45 2.5 8.0 7.0 Example 2

What is claimed is:
 1. (deleted)
 2. (deleted)
 3. (amended) A non-aqueouselectrolytic solution secondary cell, comprising: a non aqueouselectrolytic solution including an additive for the non-aqueouselectrolytic solution secondary cell that contains a phosphazenederivative represented by formula (1), and a supporting salt: an anode;and a cathode, wherein the content of the phosphazene derivative in thenon-aqueous electrolytic solution is 5 to 80 vol %. (PNF₂)_(n)   formula(1) in which n represents 3 to
 14. 4. (amended) A non-aqueouselectrolytic solution secondary cell, comprising: a non aqueouselectrolytic solution including an additive for the non-aqueouselectrolytic solution secondary cell that contains a phosphazenederivative represented by formula (1), and a supporting salt: an anode;and a cathode, wherein the content of the phosphazene derivative in thenon-aqueous electrolytic solution is 5 to 75 vol %: (PNF₂)_(n)   formula(1) in which n represents 3 to
 14. 5. (amended) The cell of claim 3,wherein viscosity of the non-aqueous electrolytic solution at 25° C. isno more than 4.0 mPa.s (4.0 cP).
 6. (amended) The cell of claim 3,wherein the non-aqueous electrolytic solution includes an aproticorganic solvent.
 7. The cell of claim 6, wherein the aprotic organicsolvent includes at least one of cyclic and chain ester compounds. 8.(deleted)
 9. (deleted)
 10. (amended) A non-aqueous electrolytic solutionelectric double layer capacitor, comprising: a non aqueous electrolyticsolution including an additive for the non-aqueous electrolytic solutionelectric double layer capacitor that contains a phosphazene derivativerepresented by formula (1), and a supporting salt: an anode; and acathode, wherein the content of the phosphazene derivative in thenon-aqueous electrolytic solution is 3 to 80 vol %. (PNF₂)_(n)   formula(1) in which n represents 3 to
 14. 11. (amended) A non-aqueouselectrolytic solution electric double layer capacitor, comprising: a nonaqueous electrolytic solution including an additive for the non-aqueouselectrolytic solution electric double layer capacitor that containstherein a phosphazene derivative represented by formula (1), and asupporting salt: an anode; and a cathode, wherein the content of thephosphazene derivative in the non-aqueous electrolytic solution is 3 to75 vol %. (PNF₂)_(n)   formula (1) in which n represents 3 to
 14. 12.(amended) The capacitor of claim 10, wherein viscosity of thenon-aqueous electrolytic solution at 25° C. is no more than 4.0 mPa.s(4.0 cP).
 13. (amended) The capacitor of claim 10, wherein thenon-aqueous electrolytic solution contains therein an aprotic organicsolvent.
 14. The capacitor of claim 13, wherein the aprotic organicsolvent includes at least one of cyclic and chain ester compounds.